In recent years, with advance in functionality and diversification of various electronic devices such as mobile phones or car navigation systems, in many electronic devices, light-transmitting touch panels are mounted on front surfaces of display elements such as liquid crystal display elements, and operators operate the devices by touching the touch panels with her/his fingers or the like while viewing displays of display elements on rear surfaces through the touch panels to switch various functions of the devices. There is a demand for electronic devices that can be easily used and reliably operated.
FIG. 4 is an exploded perspective view of conventional touch panel 500. Upper substrate 1 is a film-like light-transmitting substrate having substantially a rectangular shape. Light-transmitting almost-strip-shaped upper conductive layers 2 made of, e.g. indium tin oxide are arranged in forward and backward directions on an upper surface of upper substrate 1. Ends of upper electrodes 3 are connected to respective one of ends of upper conductive layers 2, and other ends of upper electrodes 3 extend to a right end of a periphery of upper substrate 1. Upper electrode 3 is made of conductive material, such as silver or carbon.
Lower substrate 4 is a film-like light-transmitting substrate having an almost rectangular shape. Light-transmitting almost-strip-shaped lower conductive layers 5 made of, e.g. indium tin oxide are arranged on an upper surface of lower substrate 4 in a lateral direction perpendicular to upper conductive layers 2. Ends of lower electrodes 6 are connected to ends of lower conductive layers 5, respectively, and respective other ends of lower electrodes 6 extend to a right end of a periphery of lower substrate 4. Lower electrode 6 is made of conductive material, such as silver or carbon.
Transparent plate 7 is made of insulating resin, has substantially a rectangular shape, and is light-transmittable. A center portion on the upper surface of transparent plate 7 having substantially a dome shape projects upward, thus having convex part 7A having a curved surface in forward and backward directions and a curved surface in lateral directions is formed on an upper surface of transparent plate 7. Transparent plate 7 has a flat lower surface. Transparent plate 7 is stacked on the upper surface of upper substrate 1, and upper substrate 1 is stacked on the upper surface of lower substrate 4. The substrates and the plate are bonded to each other with an adhesive agent, thereby providing touch panel 500.
Touch panel 500 is disposed on a front surface of a display element, such as a liquid crystal display, to be installed into an electronic device. Upper electrodes 3 and lower electrodes 6 extending to the right end of the periphery of the touch panel 500 are electrically connected to the electronic circuit of the electronic device with a flexible wiring board and a connector.
While a voltage is applied sequentially from the electronic circuit to upper electrodes 3 and lower electrodes 6, when an operator touches the upper surface of transparent plate 7 with her/his finger according to a display of the display element, an electric capacitance between upper conductive layer 2 and lower conductive layer 5 changes at a touched position. The electronic circuit detects the position based on the change of the capacitance, and switches various functions of the electronic device.
For example, while plural menus are displayed on the display element, when an operator touches the upper surface of transparent plate 7 on a desired menu with her/his finger, an electric charge is lead to the finger to change a capacitance between upper conductive layer 2 and lower conductive layer 5 at the touched position on the touch panel. The electronic circuit detects the change of the capacitance to select of the desired menu.